QCD Coupling from a Nonperturbative Determination of the Three-Flavor ?? Parameter

Abstract

We present a lattice determination of the Λ parameter in three-flavor QCD and the strong coupling at the Z pole mass. Computing the nonperturbative running of the coupling in the range from 0.2 to 70 GeV, and using experimental input values for the masses and decay constants of the pion and the kaon, we obtain ΛMS¯(3)=341(12) MeV. The nonperturbative running up to very high energies guarantees that systematic effects associated with perturbation theory are well under control. Using the four-loop prediction for ΛMS¯(5)/ΛMS¯(3) yields αMS¯(5)(mZ)=0.11852(84).